The problem of disposal of bulky solid waste material is receiving increasing attention. Preferably, waste material, such as old appliances and tires, is reduced in size in an early stage of waste disposal. Among the reasons for size reduction are volume densification and the requirements of subsequent processing, such as burial or combustion.
For example, sometimes discarded tires are segmented prior to transportation to a dump site or to a processing plant for recycling tires into fuel. The dimensions of a tire make it difficult to stack tires in a low volume. In transporting tires, motor trucks will often carry only one-half a full load by weight. Since a motor truck operated at less than a full load costs very nearly as much as a truck which is at its load capacity, the cost effectiveness of transporting tires may be increased by volume densification prior to shipment.
Apparatus for shredding rubber tires and other waste materials are known. U.S. Pat. Nos. 4,607,800 to Barclay, 4,374,573 to Rouse et al. and 3,931,935 to Holman disclose machines for size reduction of waste. Such machines include counter-rotating shearing wheels which overlap for material shearing cooperative engagement. Because of the difficulty in cutting solid waste, extremely hard materials must be employed in constructing shearing wheels. Generally, a chrome alloy tool steel is used. Such materials are very expensive and, given the low profit margin of waste recycling, are often cost prohibitive.
German Pat. No. 3,413,614 discloses a machine for cutting up tires which reduces the cost of manufacturing cutting wheels. Each wheel has a core made of tough high tensile steel with the blade edges being formed from a layer of wear-resistant metal which is deposited onto the steel core by welding. However, the German patent emphasizes a cutting action rather than the shearing action of the above-identified U.S. patents. A cutting action is only sufficient in a limited number of waste reduction applications. Additionally, the cutting wheels require complete replacement upon wear of the blades. The industrial goal for durability of cutting wheels is 1000 hours. Typically, however, such wheels must be replaced every four to six work weeks at a cost of thousands of dollars.
The patents to Rouse et al. and Holman, in comparison, teach overlapping shingle-type strips about the circumferential periphery of a cutter wheel. The strips are made of chrome alloy tool steel, while the core of the cutter wheel is constructed of steel. After the strips have worn to a point at which the spacing between adjacent wheels has increased to 0.03 inches, the strips are discarded and replaced with new shingle-type strips. Thus, the strips permit continuing use of a cutter wheel with only the strips needing regular replacement. However, because the shingle-type strips are in overlapping relation to each other so that they must be removed individually, the down time of a waste shearing machine during strip replacement is lengthy. Moreover, worn strips cannot be sharpened for reuse.
It is an object of the present invention to provide a shearing wheel which substantially reduces the down-time required in restoring a worn shearing wheel to a proper operating condition. It is a further object to provide such a shearing wheel which permits resharpening after the hardened shearing material of the wheel has worn.